The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
Communication links operating under the IEEE 802.3 standard, commonly referred to as “Ethernet,” may include a feature known as Energy-Efficient Ethernet (“EEE”) that allows link partners to save energy, if the physical layer transceivers (PHYs) of both link partners support EEE at the speed at which the link is established.
An EEE link achieves energy savings by having each PHY enter a low-power-idle (LPI) mode. When a PHY is in LPI mode, the PHY cannot transmit or receive regular data signals, but only “sleep” and “refresh” (or “wake”) signals. Each PHY on an EEE link will enter LPI mode after a predetermined interval (the LPI “enter time-out”) of inactivity following a “sleep” signal sent by that PHY (to give time for any link-partner PHY that wants to transmit to so do before the first PHY times out and enters LPI mode). When one of the PHYs on a link that is in LPI mode needs to start transmitting, it first transmits a “refresh” signal, and then waits for a predetermined period (the LPI “exit time-out”) to elapse (to give time for the link-partner PHY to also awaken) before it exits from LPI mode and starts transmitting regular data traffic. Values of the enter time-out and the exit time-out are specified in a type-length-value (TLV) frame according to the link-layer discovery protocol (LLDP) set forth in the IEEE 802.3az standard.
The PHYs on a link exchange EEE capabilities as part of the auto-negotiation process during which the link is set up. During that auto-negotiation process, each respective PHY transmits to each other PHY on the link its own EEE capabilities, including the speed(s) at which that respective PHY is capable of supporting an EEE link. Each PHY stores the EEE capabilities of each other PHY on the link, but only to the extent that the PHY itself is capable of EEE. The host to which any local PHY on the link is connected can examine the data identifying those capabilities of remote PHYs as stored by each local PHY of that host, and can use that capability data to rearrange links between itself and other hosts into a more efficient configuration, but that data, stored by individual local PHYs, identifying EEE capabilities of remote PHYs, will not include data regarding EEE capabilities of a link-partner PHY of a local PHY that that local PHY cannot itself support.